Method of and apparatus for securing constancy in the light of vacuum-tubes.



F. SCHRD'TER.

METHOD OF AND APPARATUS FOR SECURING CONSTANCY IN THE LIGHT 0F VACUUM TUBES.

APPLICATION FHED APR. 3. 1913.

1,172,568., Patented Feb. 22,1916.

2 SHEETS-SHEET I.

F. SCHRUTER.

METHOD OF AND APPARATUS FOR SECURING CONSTANCY IN THE LIGHT 0F VACUUM TUBES.

' APPLICATION FILED APR. 3.19I3.

l wgfifio Patented Feb.22,1916.

2 SHEETS$HEET 2.

FRITZ SCHRfiTER, OF BERLIN-WILMERSDORF, GERMANY.

EETHOD OE AND APPARATUS FOR SECURING CONSTANCY IN THE LIGHT F VACUUM- TUBES.

Specification of Letters Patent.

Patented Feb. 22, 1916.

Application filed Apr-113, 1913. Serial No. 758,527.

To all whomc't may concern:

Be it known that I, Dr. FRITZ SCHRGTER,

a subject of the King of Prussia, in the German; Empire, residing at Berlin-Wilmersdorf, in the Kingdom of Prussia, German Empire, .have invented certain new and useful Improvements in the Method of and Apparatus for Securing Constancy in the from white to bluish, and in the case of Light of Vacuum-Tubes, of which the following is a specification.

My invention relates to improvements in the method of and apparatus for securing constancy in the light of vacuum tubes.

The change of color of the light of a vacuum tube during discharge is essentially due to three causes: (1) the electrodes and the wall of the tube may give off gaseous impurities which cause an increase in the pressure of the gas, and cause the light-giv ing gase. 9., helium or -neonto behave in a remarkable manner, its characteristic light being extinguished by the presence of small quantities of foreign gases; (2) an absorption of the light-giving gas accompanied by a diminution of pressure may take place owing to the vaporization or pulverization of the electrodes, whereby a change in the color of the light is produced-e. 9., in the case of nitrogen from yellow to pink, in the case of carbon di-oxid helium from ytllow to green; and (3) gaseous impurities may have been left behind by incomplete exhaustion of the tube before it was filled with the desired lightgiving gas, a'small percentage of these impurities changing the color of the light of dischargee. 9., the presence of air causing nitrogen to give a white light and the presence of water vapor causing neon to give a bluish light, the characteristiccolors given by these gases in their pure state being yellow and orange respectively. In order to produce and maintain the characteristic color, in these cases, purification of the lightgiving gas is necessary in the first and third cases, and its regeneration in I the second case. 7

It has already been proposed to purify the light-giving gas by highly-colored wood charcoal or certain chemical substances which are so placed in the tube as to be heated by the heat of the discharge and are the .light tube are employed, which auto-.- matically admit gas into the tube when a change in the resistance of the tube takes place. These means, however, operate in a one-sided and incomplete manner.

The present invention has for object to provlde a method and an apparatus for aifectlng vacuum-light tubes in such a manner that the above mentioned difierent causes of the changes in the color of the light can be removed at the same time. For this purpose, auxiliary electrodes .are used in the tube, whichcome into operation under certain circumstances, and, by the pulverization or vaporization of the cathode of these auxiliary electrodes under the influence of the heat of discharge, cause the takmg up of the light-changing impurities, and so render them inefiective, or give up the heat they receive from the charge to gas evolving substances, which by evolving gas prevent the increase of the terminal potential difference and the consequent change of color of the light. Such auxiliary electrodes have already been used in Rontgen tubes for preventing. the hardening of the tube, the arrangement being such that whenever the vacuum becomes too high, the discharge leaps upon an auxiliary electrode, which, owing to the heating effect of the heat of discharge, evolves a certain quantity of gas and thus regenerates the tube. This arrangement, however, works intermittently, since it is only in operation during certain periods. The auxiliary electrodes in vacuum tubes according to this invention, however, act continuously, since the change of the seat of discharge in consequence of the peculiar properties .of the small vacuum takes place continually.

In the drawings, are shown diagrammatiornron A heat of disout the invention for several cases in which internal electrodes are used. In a similar manner, however, external electrodesqcan be comployed. I

In said drawings Figure 1, is a longitudinal section of the tube, Fig. 2, is a similar section of one end of a modification of the tube showing a subsidiary electrode of a different construction, and Figs. 3 and 4 are longitudinal sections of further modifications of the tube. I The arrangement according to Fig. 1

shows a lighttub'e, which contains in its expanded portions at its ends the two main electrodes 6 and 2 In lateral extensions b and b of the tube auxiliary electrodes k and 71 are arranged. Each auxiliary electrode is electrically connected with the corresponding main electrode. The main electrodes are connected by wires in the usual manner with the secondary terminals 8 and s of an electrical generator or transformer t.

The ratio of the distances of the main and auxiliary electrodes from the points a may be chosen as desired, according to the circumstances at the time being. If thedistances a k and a k are greater than the distances at e and a e and the auxiliary electrodes have not normally a substantially smaller cathode drop, the discharge takes place between the main electrodes. As soon, however, as those main electrodes give ofi impurities which immediately increase the cathode drop of the main electrodes, the discharge is transferred to the auxiliary electrodes, and establishes itself between them since it is provided for that the cathode drop of the auxiliary electrodes cannot increase, the impurities immediately vanishing there. For this purpose the auxiliary electrodes are made of a metal which is sufliciently pulverizable or sufliciently vaporizable by the discharge proceeding therefrom to cause an absorption (occlusion) or a chemical combination of the impurities to take place at the electrodes themselves or in the metallic sublimate which they produce on the vessel wall.

The property of metallic vapors to combine with gases under the influence of the electric discharge is well-known. During electrical discharge in vacuum tubes, the metallic electrodes generally volatilize and emit vapors into the gas, which becomes combined therewith to form a solid substance. All gases do not so combine with equal ease. For instance, if rare gases contain traces of other gases such as nitrogen or carbon di-oxid, and electric discharge takes place between volatilizing aluminium electrodes in an atmosphere of such gases,

only the gaseous impurities are removed, while the rare gas in question is purified. Similarly the purification of gases, by heating and so vaporizing therein a suitable metal, and at the same time subjecting the gases to the electric discharge is known.

According to this invention the vaporization or pulverization produced by the electrical discharge is'used'with the object of purifying the light-giving gas from traces of foreign gases, but without the disadvantage of causing the darkening of the light by prolonged maintenance therein of the pulverization or vaporization and the consequent deposition of the metallic sublimate on the ,wall of the tube. This darkening would take place for example, if either the main electrodes were so arranged that they were sufliciently pulverizable or volatile to purify the gas sufficiently quickly and thoroughly, or if during the electric discharge in the light "tube, a metal were caused to undergo prolonged-vaporization by a separate and moreover inconvenient heating device. In both cases the volatilization process would proceed during the whole of the period of illumination of the tube, and the efiect would be a rapid deposition on the whole of the inner wall of the tube which would thus lose its transparency. Besides this there would be introduced the danger that the light-giving gas might soon become combined with the too rich deposit.

According to this invention the process of pulverization or vaporization is intended to take place at the auxiliary electrodes only, and very strongly at these electrodes in order to effect a rapid purification of the gas and so to maintain the light at a constant color. tomatically into operation only in cases of need, i. e., only when the color of the light tends to change and a purification by volatilization of metal is required. If the cause of the change of color of the light ceases to operate, the auxiliary electrodes automatically become inoperative, and the danger of the darkening of the whole of the light tube by prolonged volatilization and sublimation of metal is avoided.

Metals which, on the vaporization of cathodes made thereof, are well adapted to fix such impurities as hydrogen, gases containing carbon, water vapor, and nitrogen, are, for example, the alkali metals. Further the alkaline earth metals, magnesium, zinc, nickel, aluminium, and generally all metals which chemically combine with hydrogen or easily take it up in their pores, such as platinum or palladium, are suitable. The alkali metals are suitable for the object in question only after heating in vacuo for a long time, when they give off impurities themselves. They other metals give ofi completely their small gaseous contents, when they are subjected for some time at high current density to a glow discharge. This is easily eflected by allowing the discharge to travel solely between the auxiliary electrodes. While the other metals can be employed as desired in the form of wires or thin plates of desired form with the purpose of increasing the current density to the utmost degree and so producing the greatest heating effect, .the alkali metals are employed preferably in a form which is represented in Fig. 2, which shows only one end of the tube.

In the expanded portion 9 at the end of the light tube 1' is situated the main electrode e. The lateral extension I), which These. auxiliary electrodes come aullt admitted.

preferably bulges, outat (1, contains an iron electrode h which serves as a receptacle, in which some potassium or other alkali metal m is melted. On vaporization, a mirror of potassium is deposited on the wall of the dilated portion d. For the heating of the potassium either an electrical heating spiral i may be wound on the outside, or the electrode may be arranged for internal electrical heating. The heating may be efi'ected'ex ternally by bther means such as, for example, a heating bath or a flame. External electrical heating, however, has the same effect.

The mode of operation of the apparatus according to Figs. 1 and 2 is the following. The light tube is exhausted and some of the light-giving gas, for example neon, is then a The discharge first travels through the shorter pathfrom e to e As soon as these electrodesbecome Warm the impurities are expelled and on account of the accompanying increase of potential drop of e and 6?, the discharge-is transferred to 12, and 11. Immediately there are evolved at these auxiliary electrodes, vapors which absorb the impurities, whereby the pure orange color of the neon is restored, and at the same time the discharge returns to 6 and 0 because the potential drop there is again lowered owing to purification of the gas. This action is repeated automatically until the electrodes give off no more gaseous impurities, and all other impurities coming from the wall of the vessel'or gases which remained behind on the exhaustion of the tube are removed. N eon is in this process .not appreciably absorbed. In this way, by

thealternating action of the main and auxiliary electrodes, every impurity is removed andthe light of the tube is maintained constant. As soon as impurities can no more appear in the tube, the discharge takes place permanently between 6 and 6 and the auxiliary electrodes automatically go out of action. In spite of the initial prolonged alternation of the seat of discharge, the light of the light tube proper. 1' remains unchanged. The transference of the discharge to the auxiliary electrodes in the caseof an evolution of gas on the part of the main electrodes can be facilitated by artificial warming of the auxiliary electrodes.

If the same arrangement is to be used for the purpose of the regeneration of the tube, the heat appearing at the secondary electrodes on transference of the discharge is used for the purpose of heating these substances which on warming slowly evolve the light-giving gas until a small quantity of the gas is evolved, whereby the original color ofthe light is restored, so that since the apparatus works in a continuous manner, the slightest fluctuations in the color of the light are immediately counteracted. If,

for example, the light tube is filled with carbon di-oxid which, at the normal ter=' come into action,and the, substance provided there, in this case advantageously a pure bicarbonate, gives off some carbon. di-oxid which immediately cuts ofi the discharge at the auxiliary electrodes and then spreads itself throughout the tube, the normal color of the light and the-normal voltage being simultaneously restored. In the case of tubes filled with nitrogen, a suitable compound of a metal with nitrogen, as mag- .nesium nitrid, or better lithium nitrid mixed with powdered quartz, or a nitrid of an alkali metal mixed with some metal powder, a

is employed. For helium tubes eleveite mixed with some metalpowder-for example, calcium,-can be used. The tube must possess in all these cases extensions with quicklv acting drying agents. I

InFi'g. 3 another mode of connection of the tube is represented. In this case the auxiliary electrodes 72. and k are not directly connected with the source of current, but are connected together. by a metallic connection w. This connection can be either a simple wire or a suitable resistance device such as liquid or wire resistance, vacuum tube, spark-gap, or self-induction. The simple wire connection is only employed initially and is removed later. It allows the discharge to travel in the following path; from terminal 8 to e, thence directly to h through the wire 10 to 72 thence to e and to the terminal 8 An alternating current flows alternately in this and the opposite direction. I The discharge goes this way only when the surface of the auxiliary electrode is not too smalli. 6., when the cathode potential drop of the auxiliary electrodes is not too great. With this arrangement the main electrodes are caused to be rapidly and thoroughly freed from gas owing to the fact that the path of the current through the tube is shorter and closer to the main electrodes; on the other hand the auxiliary electrodes pulverize very strongly and purify the whole of the contents of the tube by I alternate heating and cooling of the auxiliary electrodes. When the main electrodes are freed from gaseous impurities, the auxiliary electrodes are for some time switched out, and the discharge is allowed to travel through the whole length of the tube in order to free the vessel wall from gaseous and all other impurities. The auxiliary electrodes are again connected together and the accumulated impurities are removed by the discharge of the auxiliary electrodes, whereupon the tube finally shows a light of a constant color, and the connecting Wire of the auxiliary electrodes may be permanently removed, whereupon the auXiliary electrodes go out of action. In other cases the auxiliary electrodes 7L and k are connected by a resistance w, which is so adjusted that the resistance to transference at the auxiliary electrodes plus the resistance of the connection is greater than the resistance possessed by the portion of the light tube between the auxiliary .electrodes, when it contains completely pure gas giving of its characteristic color. Consequently a portion or the whole of the discharge goes through the resistance w which connects the auxiliary electrodes. These auxiliary electrodes thus come into operation-21 6., they purify the gas on account of their pulverization-and the gas on restoration of the normal resistance and the consequent reestablishment of the discharge between the main electrodes, again gives its correctly colored light. The resistance connecting the auxiliary electrodes need not be removed but may remain during the whole life of the light tube, since the auxiliary electrodes k and k come into operation only when the resistance of the tube is increased by impurities. The same arrangement can be used for regulating the light which changes color through an increase of terminal potential difference which is due to a diminution in the pressure of the light-giving gas. For instance, when a vacuum whose pressure is below the point of maximum conductivity is increased, the potential drop along the light-giving column of gas becomes greater and the light consequently varies. In this case, therefore the discharge would pass through the external resistance w, whereupon suitable substances provided at the auxiliary electrodes h and 72 would give ofi' suflicient gas to decrease the drop of potential along the light-giving column of gas to such an extent as to cause the light to regain its normal color.

Fig. 4 shows an'arrangement correspond ing to Fig. 1, whereby, however, the necessary connection and disconnection of the auxiliary electrodes is effected when required (for instance, as long as opportunity for the'production of impurities in the gaseous contents of the light tube exists), not by the operation within the tube itself-- 2'. e., in the secondary circuit, but by operations in the primary circuit. In this case,

there are again in the light tube 7- the main the discharge travels along the shorter path. When the discharge travels from 71, to 71. however, the current in the tube rises on account of the purifying effect of the auxiliaryelectrodes. With this increase of the secondary current there is connected an increase of the primary current, which flows through the'two solenoids n and n besides flowing; through the choking coil 2' and the primary winding 39 of the transformer. Owing to the increase of the strength of the primary current, the iron cores 0 and 0 situated in suitably constructed high tension interrupters, are so attracted into the solenoids as to cause the disconnection of the auxiliary electrodes from the source of current at contacts is? and $6 which previously secured the connection between 8 and h (through is, I

0 and 0 and between 8 and 71.? (through 7;", c and 0 -The auxiliary electrodes be ing disconnected from the source of current, the discharge takes place through the light tube between e and 6 As soon, however, as impurities are again evolved, the primary current falls in consequence of the. decrease in strength of the secondary current and theauxiliary electrodes are again connected with the source of current at 70 and 70 by the falling of the iron cores 0 and 0 6., they again act as purifiers, un-

til they are again disconnected by the increase of the current on the removal of the impurities. This arrangement, unlike the arrangements shown in Figs. 1 to 3, enables the tube to give not only a light of constant color, but also of constant luminosity, since on the occurrence of a stronger current the path of discharge is increased and vice versa. The apparatus tends tokeep the light column proper at constant current strength. The contacts 70 and 10 owing to the high voltage employed, lie preferably in a good insulating liquid. Obviously the solenoids n and 11. may be traversed by the secondary current instead of by the primary current so that the switching .in and out will be effected directly by the strength of the current of the discharge circuit. Further, it will be clear that the auxiliary electrodes may be permanently in taneous switching out of one set of electrodes and switching in of the other set,

and vice versa, so that always only one set of electrodes, either the main electrodes only or the auxiliary electrodes only, will be switched in. Again the distance between the auxiliary electrodes can be made greater than the distance between the main electrodes. v a

I claim herein as my invention:

1. The herein described method of rendering inactive the impurities in the light giving gas which when present change the light of a vacuum tube, which consists in temporarily establishing a subsidiary discharge within the tube and causing the same to atomize a material which is adapted to render the said impurities inactive.

2. The herein described method of rendering inactive the impurities in the light giving gas which when present change the light of a vacuum tube, which consists in temporarily establishing a subsidiary discharge within the tube and causing the same ing inactive the impurities in the light'giving gas which when present change the light of a vacuum tube, which consists 1n temporaril establishing a subsidiary discharge Withln the tube and causing the same to atomize a material which isadapted to render the said impurities inactive, and simultaneously heating the said material by an external source of heat.

4:. The herein described method of rendering inactive the impurities in the light giving gas which when present change the light of a vacuum tube, which consists in providing within the tube apart from the main electrode a subsidiary electrode of suitable material susceptible of giving oil a vapor capable of rendering the said lmpurities inactive, and causing atomization of the said subsidiary electrode by means of an electrical discharge therefrom;

5. The herein described method of rendering inactive the impurities in the light giving gas which when present change the light of a vacuum tube, which consists in providing within the tube apart from the main electrodes a subsidiary electrode of suitable material susceptible of giving oil a vapor capable of rendering the said impurv ities inactive; causing atomization of the said subsidiary electrode by means" of an electrical discharge therefrom, and heating by means of the discharge from the subsidlary electrode a substance which is adapted when being thus heated to give off a gas.

which prevents an increase of the voltage and a change of the color of the light of the tube which is caused by an increase of the voltage. I

'6. The herein described method of rendering inactive the impurities in the light giving gas which when'pres'ent change the light of a vacuum tube, which consists in providing within the tube apart from the main electrodes a subsidiary electrode of suitable material susceptible of givin off a vapor capable of rendering the said impurities inactive, and causing atomization of the said subsidiary electrode by means of an electrical discharge therefrom while heating the same.

71 The herein described method of rendering inactive the impurities in the light giving gas which when present change the light of a vacuum tube, which consists in provid-' ing within the tube apart from the main electrodes 'a subsidiary electrode of suitable material susceptible of giving oil a vapor capable of rendering the said impurities inactive, causing atomization of the said subsidiary electrode by means of an electrical discharge therefrom while heating the same, and heating by means of the discharge from the subsidiary electrode a substance which is adapted when being thus heated to give off a gas which prevents an increase of the voltage and a change of the color of the light of the tube which is caused by an increase of the voltage.

8. A vacuum tube comprising a pair of main electrodes, and at least one subsidiary electrode which is mounted in the tube and normally inoperative and means for rendering said subsidiary electrode operative upon a change of the resistance of the tube caused by impurities of the gas within the tube; said subsidiary electrode, when operating, atomizing a substance which is adapted when atomized to render the said impurities inactive.

-9. A vacuum tube comprising a pair of main electrodes, and at least one subsidiary electrode which is mounted in the tube and normally inoperative and means for render- 10. A vacuum tube comprising a pair of main electrodes, at least one subsidiary electrode which is mounted in the tube and normally inoperative and means for rendering said subsidiary electrode operative upon a change of the resistance of the tube caused by impurities of the gas within the tube; said subsidiary electrode, when operating, atomizing a substance which is adapted when atomized to render the said impurities inactive, and special heating means for said substance.

11. A vacuum tube comprising a pair of main electrodes, and at least one subsidiary electrode which is mounted in the tube and normally inoperative and means for rendering said subsidiary electrode operative upon a change of the resistance of the tube caused by impurities of the gas within the tube; said subsidiary electrode consisting of a, material which is adapted to be atomized by an electrical discharge and when atomized to render the said impurities inactivef 12. A vacuum tube having a main chamber and at least one subsidiary chamber and comprising a pair of main electrodes within the main chamber, and at least one subsidiary electrode located within the sub. sidiary chamber and which is normally inoperative and means for rendering said subsidiary electrode operative upon a change of the resistance of the tube caused by impurities of the gas within the tube; said sub sidiary electrode, when operating, atomizing a substance which is adapted when atomized to render the said impurities inactive.

13. A vacuum tube comprising a pair of main electrodes, and a pair of subsidiary electrodes which are mounted in the tube and normally inoperative; means for rendering said subsidiary electrodes operative upon a change of a resistance of the tube caused by impurities of the gas Within the tube; said subsidiary electrodes, when operating, atomizing a substance which is adapted when atomized to render the said impurities inactive.

14. A vacuum tube having a main chamber and a pair of subsidiary chambers and comprising a pair of main electrodes within said main chamber, and a pair of subsidiary electrodes located one within each subsidiary chamber and which are normally inoperative; means for rendering said subsidiary electrodes operative upona change of the resistance of the tube caused by impurities of the gas within the tube; said subsidiary electrodes, when operating, atomizing a substance which is adapted when atomized to render the said impurities inactive.

In testimony whereof I afiix my signatur in presence of two witnesses.

DR. FRITZ SCHROTER.

Witnesses:

HENRY HASPER, WOLDEMAR HAUPT. 

